JP6180480B2 - Sheet feeding apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a sheet feeding apparatus that separates and feeds sheets, and an image forming apparatus including the sheet feeding apparatus.

  In general, a sheet feeding device provided in an image forming apparatus is arranged downstream of a feeding roller after separating and feeding sheets stacked on a stacking member such as a cassette one by one by a feeding roller. Deliver the sheet to the conveying member.

  As such a sheet feeding device, it is possible to input a paper size via a paper feeding roller for feeding out the paper stacked on the paper feeding tray, a registration roller for conveying the paper downstream of the paper feeding roller, and an operation panel. A sheet feeding apparatus including a control unit is known (see Patent Document 1). In this paper feeding device, after the rotation of the paper feeding roller is started, the driving of the paper feeding roller is stopped at the timing when the trailing edge of the paper reaches the paper feeding roller based on the length of the paper in the feeding direction. . In this paper feeding device, since the paper feeding roller is driven even after the paper reaches the registration roller, the paper conveyance force by the registration roller is supplemented.

JP 2001-348129 A

  By the way, the structure which isolate | separates a sheet | seat using a separation roller as a sheet feeding apparatus is known. That is, a feeding roller that conveys a sheet in the feeding direction, a separation roller that is pressed against the feeding roller and driven in a direction opposite to the feeding direction via a torque limiter, and drives the feeding roller and the separation roller Driving means. In this configuration, at least while the feeding roller is driven, a driving force is input to the separation roller in order to improve the sheet separation performance.

  In such a sheet feeding device, like the paper feeding device described in Patent Document 1, after the sheet reaches the conveying means downstream of the feeding roller, the driving of the feeding roller is continued, and the conveying means It is conceivable to assist the conveyance of the sheet. As a result, it can be expected that the sheet can be conveyed stably while preventing double feeding of the sheet.

  However, in such a configuration, when feeding a sheet, the separation roller sometimes vibrates by repeating forward rotation and reverse rotation little by little. The vibration of the separation roller tends to increase in amplitude when a sheet with low rigidity is conveyed as compared with when a sheet with high rigidity is conveyed. When vibration with a large amplitude is continued, there is a possibility that annoying vibration sound is generated.

  SUMMARY An advantage of some aspects of the invention is that it provides a sheet feeding apparatus that can stably convey a sheet and can reduce vibration noise during operation, and an image forming apparatus including the sheet feeding apparatus.

A sheet feeding apparatus according to the present invention includes a feeding roller that transports a sheet in a feeding direction, a driving unit that drives the feeding roller, and a separation nip portion that sandwiches the sheet between the feeding rollers. A separation roller that is connected to the driving means via a torque limiter and is driven in a direction opposite to the feeding direction; and a conveyance nip that sandwiches the sheet downstream of the separation nip portion in the feeding direction. And a conveying unit that conveys the sheet, and a control for stopping the driving of the driving unit in a state where the sheet is sandwiched between the separation nip unit and the conveying nip unit after driving of the driving unit is started. and means, in the first control mode is set to transport the first sheet, before at a timing later than the second control mode conveying the first second sheet basis weight than the sheet is small And a Ru control means stops the driving of the driving means, characterized in that.

The sheet feeding apparatus according to the present invention includes a separation roller that sandwiches a sheet between a feeding roller that conveys the sheet in the feeding direction, a driving unit that drives the feeding roller, and the feeding roller. A separation roller connected to the driving means via a torque limiter and driven in a direction opposite to the feeding direction, and sandwiching the sheet downstream of the separation nip portion in the feeding direction A conveyance unit having a conveyance nip and conveying the sheet, and driving of the driving unit are started, and then driving of the driving unit is stopped in a state where the sheet is sandwiched between the separation nip unit and the conveyance nip unit. a control means for, in the first control mode is set to transport the first sheet, a timing later than the second control mode for transferring the rigidity is lower than the first sheet second sheet And a Ru control means stops the driving of said driving means, characterized in that.

  According to the sheet feeding device of the present invention, it is possible to stably convey a sheet and reduce vibration noise during operation.

1 is a schematic configuration diagram illustrating an image forming apparatus according to a first embodiment. FIG. 3 is a perspective view illustrating a main part of the sheet feeding apparatus according to the first embodiment. FIG. 5 is a schematic diagram for explaining the operation of the sheet feeding device when a sheet having high rigidity is conveyed. FIG. 10 is a schematic diagram for explaining the operation of the sheet feeding device when a sheet having low rigidity is conveyed. The control block diagram which concerns on 1st Embodiment. The figure which combined the timing chart of the 1st control mode concerning a 1st embodiment with the diagram showing the position of a sheet (when sheet length is large). The figure which combined the timing chart of the 2nd control mode which concerns on 1st Embodiment with the diagram showing the position of a sheet | seat (when sheet length is large). The figure which combined the timing chart of the 1st control mode concerning a 1st embodiment with the diagram showing the position of a sheet (when sheet length is small). The figure which combined the timing chart of the 2nd control mode which concerns on 1st Embodiment with the diagram showing the position of a sheet | seat (when sheet length is small). 6 is a flowchart of a sheet feeding operation according to the first embodiment. 10 is a flowchart of a sheet feeding operation according to the second embodiment. The figure which combined the timing chart which concerns on 3rd Embodiment with the diagram showing the position of a sheet | seat (when sheet length is large). The figure which combined the timing chart which concerns on 3rd Embodiment with the diagram showing the position of a sheet | seat (when sheet length is small). 10 is a flowchart of a sheet feeding operation according to the third embodiment. The figure which combined the timing chart which concerns on 4th Embodiment with the diagram showing the position of a sheet | seat. 10 is a flowchart of a sheet feeding operation according to a fourth embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, it is assumed that the positional relationship between the top, bottom, left, and right is expressed with reference to the state of the image forming apparatus viewed from the front (the viewpoint in FIG. 1).

<First Embodiment>
[Image forming apparatus]
An image forming apparatus 201 according to the first embodiment is an image forming apparatus using a full-color laser beam printer as an example, as schematically illustrated in FIG. The image forming apparatus 201 includes an image forming unit 201B that forms an image on a sheet P, a fixing unit 220 that fixes an image on the sheet P, and the like inside an apparatus main body 201A (printer main body) that is an image forming apparatus body. . Above the apparatus main body 201A, an image reading apparatus 202 that reads image data of a document is disposed in a posture in which the document placement surface is substantially horizontal. A discharge tray 230 for discharging the sheet P is provided between the image reading apparatus 202 and the apparatus main body 201A. The apparatus main body 201A is provided with a sheet feeding unit 201E that feeds the sheet P to the image forming unit 201B. The sheet feeding unit 201E includes sheet feeding devices 100A, 100B, 100C, and 100D that are disposed below the apparatus main body 201A, and a manual feeding device 100M that is disposed on the right side of the apparatus main body 201A. .

  The image forming unit 201B as an image forming unit is a so-called four-drum full-color image forming unit including a laser scanner 210, four process cartridges 211, and an intermediate transfer unit 201C. These process cartridges form toner images of respective colors of yellow (Y), magenta (M), cyan (C), and black (K). Each process cartridge 211 includes a photosensitive drum 212 (photoconductor), a charger 213, a developing device 214, a cleaner (not shown), and the like. Note that a toner cartridge 215 containing toner of each color is detachably attached to the apparatus main body 201A above the image forming unit 201B.

  The intermediate transfer unit 201C is configured by winding an intermediate transfer belt 216 as an intermediate transfer member around a driving roller 216a, a tension roller 216b, and the like, and is disposed above the four process cartridges 211. The intermediate transfer belt 216 is disposed so as to be in contact with the photosensitive drum 212 of each process cartridge 211, and is rotated counterclockwise (in the direction of the arrow Q) by a driving roller 216a driven by a driving unit (not shown). Driven. The intermediate transfer unit 201 </ b> C includes a primary transfer roller 219 that contacts the inner peripheral surface of the intermediate transfer belt 216 at a position facing each photosensitive drum 212, and a nip portion between the intermediate transfer belt 216 and the photosensitive drum 212. As shown, a primary transfer portion t1 is formed. Further, the image forming unit 201B includes a secondary transfer roller 217 that contacts the outer peripheral surface of the intermediate transfer belt 216 at a position facing the driving roller 216a. As a nip portion between the secondary transfer roller 217 and the intermediate transfer belt 216, a secondary transfer portion t2 to which the toner image carried on the intermediate transfer belt 216 is transferred to the sheet P is formed.

  In each process cartridge 211 configured as described above, an electrostatic latent image is drawn on the surface of the photosensitive drum 212 by the laser scanner 210, and then toner is supplied from the developing device 214 to make it negative. A charged toner image of each color is formed. By applying a positive transfer bias voltage to the primary transfer roller 219, these toner images are sequentially multiplex-transferred (primary transfer) to the intermediate transfer belt 216 at each primary transfer portion t1, and intermediate A full color toner image is formed on the transfer belt 216.

  In parallel with such a toner image forming process, the sheet P fed from the sheet feeding unit 201E is transported toward the registration roller pair 240, and skew correction is performed by the registration roller pair 240. The registration roller pair 240 conveys the sheet P to the secondary transfer portion t2 at a timing that matches the transfer timing of the full-color toner image formed on the intermediate transfer belt 216. The toner image carried on the intermediate transfer belt 216 is secondarily transferred onto the sheet P at the secondary transfer portion t2 by applying a positive transfer bias voltage to the secondary transfer roller 217.

  The sheet P to which the toner image has been transferred is heated and pressurized in the fixing unit 220, and the color image is fixed to the sheet P. The fixing unit 220 includes a fixing roller 220a, 220b pressed against the fixing roller 220b, and a heating unit (heater) (not shown), and the sheet P at a speed corresponding to the image forming speed in the secondary transfer unit t2. Transport. The sheet P on which the image is fixed is discharged to the discharge tray 230 by the discharge roller pair 225 and stacked. When images are formed on both sides of the sheet P, the sheet P passes through the fixing unit 220 and is then switched back by a reversing roller pair 222 that can be rotated in the normal direction. Then, the sheet P is conveyed again to the image forming unit 201B via the reconveying path R, and an image is formed on the back surface.

[Sheet feeding device]
Next, the configuration of the sheet feeding apparatus will be described using the sheet feeding apparatus 100A as an example. Note that the sheet feeding devices 100B, 100C, and 100D arranged below the sheet feeding device 100A are configured in the same manner as the sheet feeding device 100A, and thus the description thereof is omitted. Further, when expressing the rotation direction of the rotating member (roller member) in contact with the sheet P, the direction along the feeding direction of the sheet P is referred to as “feeding direction”, and when the direction is opposite to the feeding direction, “ "Return direction".

  As shown in FIG. 2, the sheet feeding device 100 </ b> A includes a feeding cassette 7, a feeding unit 1, and a drawing roller pair 8 (see FIG. 3). A feeding cassette 7 serving as a stacking unit on which sheets P are stacked is housed in the apparatus main body 201A so as to be able to be pulled out, and includes a side end regulating plate 71, a rear end regulating plate (not shown), and the like. The sheets P stacked on the feeding cassette 7 are positioned in the feeding direction (the direction of the arrow Fd) by being abutted against the cassette wall 7a by the rear end regulating plate, and in the width direction by the side end regulating plate 71. Positioned.

  A feeding unit 1 that separates and transports the sheets P stacked on the feeding cassette 7 one by one, a pickup roller 2, a feed roller 3 (feeding roller), a retard roller 4 (separating roller), and a drive And a mechanism 6. The pickup roller 2, the feed roller 3, and the retard roller 4 have a posture in which the axial direction is directed to the width direction of the sheet P (the depth direction of the apparatus main body 201 </ b> A), and the pickup roller shaft 2 b, the feed roller shaft 3 a, and the retard roller shaft 4a is supported respectively.

  The feed roller shaft 3a is rotatably supported by a frame member (not shown) that forms a support frame of the feeding unit 1, and also supports the feed roller 3 so as to be rotatable. The retard roller shaft 4a is disposed in parallel with the feed roller shaft 3a, holds the retard roller 4 at a position facing the feed roller 3, and is urged by an urging member (not shown) to cause the retard roller 4 to feed the feed roller 3. Pressure contact. The pickup roller shaft 2b is attached to a pickup arm 2a that can rotate in the vertical direction about the feed roller shaft 3a, and supports the pickup roller 2 so as to be rotatable.

  The drive mechanism 6 includes a gear group (6a to 6g), a torque limiter 5, and the like, and distributes the driving force of a feed motor M1 as drive means provided in the apparatus main body 201A to each roller of the feed unit 1. An output gear 6a provided on the output shaft of the feed motor M1 meshes with an input gear 6b provided at one end of the feed roller shaft 3a, and rotates the feed roller 3 in a direction along the feed direction (feed direction). Let A distribution gear 6c is provided on the other side of the feed roller shaft 3a, and the rotation of the distribution gear 6c is transmitted to a gear 6e provided on the pickup roller shaft 2b via a gear 6d supported on the pickup arm 2a. Accordingly, the pickup roller 2 is rotationally driven in the feed direction simultaneously with the feed roller 3.

  The pickup arm 2a is connected to an urging means (not shown), a position where the pickup roller 2 can contact the uppermost sheet P of the sheet bundle loaded on the feeding cassette 7, and the uppermost sheet. It is configured to be movable to a position away from P. A one-way clutch (not shown) is provided between the feed roller 3 and the feed roller shaft 3a and between the pickup roller 2 and the pickup roller shaft 2b. That is, the feed roller 3 and the pickup roller 2 are configured to be idled in the feed direction.

  A gear 6g provided on the retard roller shaft 4a is connected to an input gear 6b via an idle gear 6f, and receives a rotation in the return direction, which is a direction against the sheet P feeding direction. The torque limiter 5 is disposed between the retard roller shaft 4 a and the retard roller 4. The torque limiter 5 transmits the driving force of the retard roller shaft 4a to the retard roller 4, and slips when a torque of a predetermined amount or more acts, so that the retard roller 4 is fed to the retard roller shaft 4a in the feed direction. Allows relative rotation.

  As shown in FIG. 3, the drawing roller pair 8 as a conveying unit that receives and conveys the sheet P from the feeding unit 1 includes a drawing roller 8 a and a counter roller 8 b. The drawing roller 8a is disposed in parallel with the axial direction of the feed roller 3, and is rotationally driven in the feeding direction by a drawing motor M2 (see FIG. 5) provided in the apparatus main body 201A. The opposing roller 8b forms a drawing nip portion N2 (conveying nip portion) that sandwiches the sheet P with the drawing roller 8a, and rotates in the feed direction as the drawing roller 8a rotates. The drawing nip portion N2 is located downstream of the separation nip portion N1 formed between the feed roller 3 and the retard roller 4 in the sheet P feeding direction (the direction of the arrow Fd).

  A feeding sensor 12 serving as a sheet detecting unit capable of detecting the sheet P is disposed between the feed roller 3 and the drawing roller 8a in the feeding direction. As the feeding sensor 12, for example, an optical sensor including a light receiving unit that can detect light emitted from the light emitting unit and a flag member that can contact the sheet P and shield the light receiving unit is used. An ON signal is issued when passing through a detection position near the sensor. Further, a registration sensor 15 capable of detecting the sheet P is disposed in the vicinity of the upstream side of the registration roller pair 240 downstream of the drawing roller pair 8 in the conveying direction (see FIG. 1).

[Sheet feeding operation]
Next, an outline of the sheet feeding operation of the sheet feeding apparatus 100A configured as described above will be described with reference to FIGS. However, a detailed control flow of the sheet feeding operation will be described later. FIG. 3 shows a sheet feeding operation when a relatively stiff sheet is transported, and FIG. 4 shows a sheet feeding operation when a relatively stiff sheet is transported. However, the rigidity of the sheet is the degree (stiffness) of the bending rigidity of the sheet, and indicates the value (Clark stiffness, Taber stiffness) measured by a test method such as the Clark method or the Taber method.

  As shown in FIG. 3, in a state where the sheet P is stacked on the feeding cassette 7, the front end, which is the downstream end in the feeding direction (the direction of the arrow Fd), is held at a position close to the cassette wall 7a. When feeding the sheet P, the pickup roller 2 is pressed against the uppermost sheet P1 at the contact position located upstream of the separation nip portion N1, and the driving of the feeding motor M1 is started in this state. Then, the sheet P1 is fed out in the direction of the arrow Fd by the pickup roller 2, reaches the separation nip portion N1, and is conveyed toward the drawing nip portion N2 by the feed roller 3.

  Here, when only the uppermost sheet P1 enters the separation nip portion N1, torque in the feeding direction acts on the retard roller 4 via the sheet P1. Then, slip occurs in the torque limiter 5, and the retard roller 4 rotates in the feed direction against the driving force of the retard roller shaft 4a. On the other hand, when a plurality of sheets P1 and P2 (two sheets in FIG. 3) enter the separation nip portion N1, the retard roller 4 rotates in the return direction according to the driving force of the retard roller shaft 4a. To do. In other words, the torque capacity of the torque limiter 5 is set to a value larger than the frictional force that can be generated between the overlapping sheets P1 and P2. As a result, the uppermost sheet P1 is conveyed toward the drawing nip portion N2, and the sheet (P2) other than the uppermost sheet is pushed back to the upstream side of the separation nip portion N1 to eliminate the double feed state.

  When the front end of the sheet P1 reaches the drawing nip portion N2, the sheet P1 is nipped by the drawing roller pair 8 driven by the drawing motor M2, and is conveyed upward in the apparatus main body 201A. Thereafter, the sheet P1 reaches the registration roller pair 240 positioned downstream of the drawing roller pair 8 to correct skewing, and is conveyed to the secondary transfer unit t2.

  Here, a phenomenon that occurs when the stiffness of the sheet P is low will be described with reference to FIG. A sheet feeding apparatus 100A shown in FIG. 4 shows a state in the middle of a sheet feeding operation for feeding sheets Q1, Q2 having lower rigidity than the sheets P1, P2 shown in FIG. That is, after the sheet feeding device 100A starts driving the feeding motor M1 and starts conveying the uppermost sheet Q1, the sheet Q1 reaches the drawing nip portion N2, and the separation nip portion N1 and the drawing nip portion N1. It is in a state of being sandwiched between the nip portions N2.

  FIG. 4 shows a state in which a sheet other than the uppermost sheet (multifeed sheet Q2) has entered the separation nip portion N1 due to friction between the sheets. When the feeding motor M1 starts driving in this state, the retard roller 4 starts to rotate in the returning direction R2, and pushes the double feeding sheet Q2 back to the upstream side of the separation nip portion N1. At this time, the multi-feed sheet Q2 is pressed against the pickup roller 2 via the sheet Q1, and is restricted from moving in the direction opposite to the feeding direction. For this reason, the multi-feed sheet Q2 having low rigidity is in a buckled state between the pickup roller 2 and the separation nip portion N1, as indicated by a broken line q2.

  When the front end of the multi-feed sheet Q2 is pushed back from the separation nip portion N1, the retard roller 4 rotates with the sheet Q1 and resumes rotation in the feed direction R1. Then, the multi-feed sheet Q2 again enters the separation nip portion N1 due to the frictional force received from the sheet Q1 and its own restoring force. As the multifeed sheet Q2 repeats the operation of entering the separation nip portion N1 and the operation of being pushed back from the separation nip portion N1, the retard roller 4 alternates minute rotations in the feed direction R1 and the return direction R2. It will be in the state which performs the operation | movement (rotation vibration) repeated. The rotational vibration of the retard roller 4 is continuously generated when the front end of the multi-feed sheet Q2 is in a position where it can enter the separation nip portion N1 and the driving force in the returning direction is input to the retard roller 4. obtain. If the rotational vibration of the retard roller 4 continues, it may be perceived as an irritating vibration sound.

  The amplitude of such rotational vibration tends to change depending on the material of the sheet conveyed by the sheet feeding device and the conveyance speed (feed speed) when the sheet is conveyed by the feed roller 3. That is, when the rigidity (rigidity) of the sheet is low, the amplitude of the rotational vibration tends to be larger than when the rigidity of the sheet is high. For this reason, the smaller the basis weight of the sheet or the smaller the thickness of the sheet, the larger the amplitude of the rotational vibration. Further, when the feeding speed is high, the amplitude tends to be larger than when the feeding speed is low.

[Select control mode]
Therefore, the sheet feeding apparatus 100A according to the present embodiment has a first control mode in which the feeding motor M1 is stopped at a relatively late timing and a second control mode in which the feeding motor M1 is stopped at a relatively early timing. And can be selected according to the type of sheet. Hereinafter, selection conditions for the first control mode and the second control mode by the control unit 9 will be described.

  As shown in the block diagram of FIG. 5, the control system of the image forming apparatus 201 according to the present embodiment is configured by connecting a plurality of input / output devices to a control unit 9 as control means. An operation panel 10, a size detection sensor 11, a feed sensor 12, a registration sensor 15, a timer 13 and the like are connected to the input side of the control unit 9. Further, a feed motor M1 and a drawing motor M2 are connected to the output side of the control unit 9, and the timing of driving start and stop and the output at the time of driving are controlled by the control signal of the control unit 9. . The control unit 9 can measure an elapsed time from the start of driving of the feeding motor M1, for example, using a timer 13 as a time measuring means.

  The size detection sensor 11 as the size detection means can detect the size of the sheet P set in the feeding cassette 7 by detecting the positions of the side end regulating plate 71 and the rear end regulating plate of the feeding cassette 7, for example. Is provided. However, the size of the sheet P is a length in the feeding direction (sheet length) and a length in the direction orthogonal to the feeding direction (sheet width). When a plurality of sheet feeding devices are provided, the size detection sensor 11 and the feeding sensor 12 are arranged in each sheet feeding device.

  The operation panel 10 as an input means has a liquid crystal panel exposed to the outside of the apparatus main body 201A, operation buttons, and the like, and the user can input the type of sheet P set in the feeding cassette 7 to the control unit 9 It is configured. However, the type of sheet P is a classification according to the material, basis weight, size, and presence / absence of surface processing of the sheet P, and the group of fine paper / recycled paper / OHP film / coated paper is classified according to the basis weight. Specific examples are subdivided. The type of the sheet P is input to the control unit 9 when the user selects from choices displayed on the liquid crystal panel.

  In accordance with the type of the sheet P, the control unit 9 sets a plurality of feeding speeds that are the conveying speeds of the sheets P in the sheet feeding operation and image forming speeds that are the conveying speeds of the sheets P in the secondary transfer unit t2. It is configured to be selectable from among the choices. Table 1 shows the correspondence between the type of sheet P, the feeding speed V1, and the image forming speed V2 in the examples of the present embodiment.

  As shown in Table 1, the image forming speed V2 is set to a smaller value as the basis weight of the sheet P is larger, and the feeding speed V1 is set to a value substantially proportional to the image forming speed V2. Accordingly, the total amount of heat received by the sheet P in the fixing unit 220 is increased, and the image is reliably fixed on the sheet P having a large heat capacity and a large basis weight.

  In the present embodiment, the first control mode is selected when the feeding speed V1 takes a large value, that is, when the sheet P has the first stiffness. Further, the second control mode is selected when the feeding speed V1 takes a small value, that is, when the sheet P has a second stiffness lower than the first stiffness. In the example of Table 1, the first control mode is applied when the feeding speed V1 is 150 mm / sec, and the second control mode is applied when the feeding speed V1 is 250 mm / sec or 300 mm / sec. Applies. In addition, in the structure which selects control mode according to basic weight, when it has 1st basic weight, 1st control mode is selected and the 2nd basic weight with which sheet P is smaller than 1st basic weight The second control mode is selected.

[First control mode]
Next, the sheet feeding operation when the first control mode is selected will be described with reference to FIG. However, FIG. 6 is a timing chart representing the drive control of the feeding motor M1 and the pulling motor M2, combined with a diagram representing the change in the position of the sheet P. The horizontal axis represents time, and the vertical axis represents motor output. And a position (transport distance) on the transport path. The output D of the feeding motor M1 is drawn as the peripheral speed of the feed roller 3, and the output E of the drawing motor M2 is drawn as the peripheral speed of the drawing roller pair 8. As described above, the output D of the feeding motor M1 is distributed to the feed roller 3, the retard roller 4, and the pickup roller 2.

  The theoretical line A1 in the drawing represents the front end position of the sheet P on the setting. The maximum delay line A2 represents a position assuming that the front end of the sheet P is most delayed with respect to the theoretical line A1, and is set in consideration of a tolerance of parts, a decrease in conveying efficiency due to roller wear, and the like. That is, the actual front end position of the sheet P normally passes through a region (shaded portion) surrounded by the theoretical line A1 and the maximum delay line A2. The theoretical line B1 represents the position of the rear end of the sheet P on the setting, and is calculated from the theoretical line A1 at the front end using the length L1 of the sheet P.

  As shown in FIG. 6, the feeding operation is started when the feeding motor M1 and the drawing motor M2 are started to drive at an output corresponding to the feeding speed V1 at time Tf. Then, the uppermost sheet P is fed out by the pickup roller 2, and the front end of the sheet P gets over the cassette wall 7a and starts moving toward the downstream in the feeding direction (upward in the drawing). The feeding motor M1 and the drawing motor M2 are temporarily stopped at time Ts after the sheet P reaches the registration roller pair 240, and the front end of the sheet P is abutted against the registration roller pair 240. Wait for a while.

  Then, at the time Tr when the registration roller pair 240 starts to operate in synchronization with the transfer timing in the secondary transfer portion t2, the feeding motor M1 and the drawing motor M2 are started again at the image forming speed V2. At this time, the pickup roller 2 and the feed roller 3 are rotationally driven in the feeding direction, so that the conveyance of the sheet P by the drawing roller pair 8 and the registration roller pair 240 is assisted.

  Thereafter, the feeding motor M1 is stopped at time T1 when the sheet P reaches the first position. However, the first position is a sheet position where the rear end of the sheet P is upstream by a predetermined distance (for example, 10 mm) from the contact position (pickup position) of the pickup roller 2. More specifically, the control unit 9 measures the driving time of the feeding motor M1 using the ON signal of the feeding motor M1 at the time Tr as a trigger, and the sheet P reaches the first position under the image forming speed V2. The required time (control time X1) until this is calculated. Then, an OFF signal is sent to the feed motor M1 at a timing (time T1) when the drive time becomes equal to the control time X1. After the driving of the feeding motor M1 is stopped, the sheet P is continuously conveyed by the registration roller pair 240 and the drawing roller pair 8, and is conveyed to the secondary transfer unit t2.

  The stop timing for stopping the driving of the feeding motor M1 is not limited to the timing at which the rear end of the sheet P reaches 10 mm upstream from the pickup position. This stop timing is within a range in which the feeding force of the drawing roller pair 8 and the registration roller pair 240 can be effectively assisted without feeding (pickup) the sheet P overlapping the uppermost sheet P. Other timings may be used. The first position, which is the seat position at the stop timing, is preferably set in consideration of component tolerances, variations in sheet dimensions, a deviation between the set value of the motor output and the actual rotational speed, and the like. In the example to which the present embodiment is applied, it is preferable that the first position is set to a position where the rear end of the sheet P is separated from the pickup position within a range of 10 mm or more and 20 mm or less.

[Second control mode]
Next, the sheet feeding operation when the second control mode is selected will be described with reference to FIG. However, FIG. 7 is a timing chart showing the drive control of the feeding motor M1 and the pulling motor M2, combined with a diagram showing the position change of the sheet P, the horizontal axis shows time, and the vertical axis shows motor output. And a position (transport distance) on the transport path. FIG. 7 shows a sheet feeding operation when feeding a sheet P having a sheet length L1 equal to that in FIG. In the following description, elements common to the first control mode are denoted by the same reference numerals and description thereof is omitted.

  As shown in FIG. 7, the sheet feeding operation is started when the feeding motor M1 and the pulling motor M2 are started to be driven at the output of the feeding speed V1 at time Tf. Then, the uppermost sheet P is fed out by the pickup roller 2, and the front end of the sheet P starts to move downstream in the feeding direction. The feeding motor M1 is stopped at time T2 when the sheet P reaches the second position. However, the second position is a sheet position at which the front end of the sheet P is downstream by a predetermined distance (for example, 10 mm) from the drawing nip portion N2 of the drawing roller pair 8. More specifically, the control unit 9 measures the driving time of the feeding motor M1 using the ON signal of the feeding motor M1 at time Tf as a trigger, and the sheet P reaches the second position under the feeding speed V1. The required time (control time X2) until this is calculated. Then, an OFF signal is sent to the feed motor M1 at a timing (time T2) when the drive time becomes equal to the control time X2.

  Here, the first position is a sheet position in which the rear end of the sheet P is upstream by a predetermined distance from the contact position of the pickup roller 2, and the second position is a predetermined distance in which the front end of the sheet P is the drawing nip portion. It is set as the downstream sheet position. In other words, the first position is a sheet position where the central portion of the sheet P in the feeding direction is closer to the drawing nip portion N2 than the contact position of the pickup roller 2. The second position is a sheet position where the central portion of the sheet P is in a state closer to the separation nip portion N1 than the drawing nip portion N2. Accordingly, the second position is an upstream position in the feeding direction with respect to the first position, and the larger the sheet length L1, the wider the gap between the first position and the second position.

  After the driving of the feeding motor M <b> 1 is stopped, the sheet P is continuously conveyed by the drawing roller pair 8 toward the registration roller pair 240. At this time, the pickup roller 2 and the feed roller 3 are idled in the feeding direction along with the sheet P by the action of the one-way clutch. On the other hand, since the retard roller 4 is drivingly connected to the feed motor M1 via the torque limiter 5, the rotation in the feed direction is restricted. Accordingly, referring also to FIG. 4, in a state where one sheet (Q1) enters the separation nip portion N1, the retard roller 4 rotates in the feeding direction along with the sheet P1. On the other hand, when the separation nip portion N1 is in the double feed state, the retard roller 4 stops rotating and holds the sheet (Q2) other than the uppermost sheet by the frictional force, and the sheet is pulled out in the double feed state. It is prevented from being conveyed to the nip portion N2.

  The drawing motor M <b> 2 is stopped at time Ts after the sheet P reaches the registration roller pair 240, and temporarily stands by with the front end of the sheet P being abutted against the registration roller pair 240. Then, the drawing motor M2 starts to be driven again at the image forming speed V2 at the time Tr when the registration roller pair 240 starts to operate, and the sheet P is conveyed to the secondary transfer portion t2.

  The stop timing for stopping the driving of the feeding motor M1 is not limited to the timing at which the front end of the sheet P reaches 10 mm downstream from the drawing nip portion N2, but the range in which the sheet P slips and does not fall off from the drawing nip portion N2. Any other timing may be used. The second position, which is the seat position at the stop timing, is preferably set in consideration of component tolerances, variations in sheet dimensions, a deviation between the set value of the motor output and the actual rotational speed, and the like. In the example to which the present embodiment is applied, it is preferable that the second position is set to a position where the rear end of the sheet P is separated from the pickup position within a range of 10 mm or more and 20 mm or less.

[When the sheet is small]
Next, a sheet feeding operation when the size of the sheet P is smaller than that shown in FIGS. 6 and 7, that is, when the sheet length L2 is relatively small will be described with reference to FIGS. . However, the change from the sheet feeding operation when the above-described sheet length L1 is relatively large will be described, and the description of the points controlled in the same manner as when the sheet length is relatively large will be omitted. FIG. 8 and FIG. 9 are diagrams each combining a timing chart representing the drive control of the feeding motor M1 and the pulling motor M2 with a diagram representing a change in the position of the sheet P. FIG. Further, the maximum delay line B2 in FIGS. 8 and 9 represents a position assuming that the trailing edge of the sheet P is most delayed with respect to the theoretical line B1, and the conveyance efficiency decreases due to component tolerances and roller wear. Etc. are set in consideration.

  As shown in FIG. 8, when the first control mode is selected, the driving of the feeding motor M1 is stopped at the time T3 when the sheet P reaches the first position after the driving of the feeding motor M1 is started. Is done. However, the first position is a position where the rear end of the sheet P is upstream by a predetermined distance (for example, 10 mm) from the contact position of the pickup roller 2. The control unit 9 supplies the feed at the timing (time T3) when the required time (control time X1) until the sheet P reaches the first position after the ON signal is transmitted to the feed motor M1 at time Tf. An OFF signal is issued to the feed motor M1. After the driving of the feeding motor M 1 is stopped, the sheet P is continuously conveyed by the drawing roller pair 8 and reaches the registration roller pair 240.

  On the other hand, as shown in FIG. 9, when the second control mode is selected, time T4 when the sheet P reaches the second position upstream of the first position after the driving of the feeding motor M1 is started. The driving of the feeding motor M1 is stopped. However, the second position is a position where the front end of the sheet P is downstream from the drawing nip portion N2 of the drawing roller pair 8 by a predetermined distance (for example, 10 mm). The controller 9 feeds at the timing (time T4) when the required time (control time X2) until the sheet P reaches the second position after the ON signal is transmitted to the feeding motor M1 at time Tf. An OFF signal is issued to the motor M1. After the driving of the feeding motor M 1 is stopped, the sheet P is continuously conveyed by the drawing roller pair 8 and reaches the registration roller pair 240.

  Similarly to the case where the sheet length is large (L1), the sheet position (first position) when the driving of the feeding motor M1 is stopped in the first control mode is the feeding motor in the second control mode. It is downstream of the sheet position (second position) when M1 is stopped. For this reason, when the first control mode is selected, the pickup roller 2 and the feed roller 3 rotate long in a range in which the sheet P overlapping the uppermost sheet P is not fed out, and the sheet by the drawing roller pair 8 Assist P transport. On the other hand, when the second control mode is selected, the feeding motor M1 is driven at an earlier timing than the first control mode in a range in which the front end portion of the sheet P does not fall off from the drawing nip portion N2. The supply of driving force to the retard roller 4 is shut off.

[Control flow]
Next, the control process of the sheet feeding operation described above will be described with reference to the flowchart of FIG. When the sheet P is stacked on the feeding cassette 7 and stored in the apparatus main body 201A, the control unit 9 detects the size of the sheet P using the size detection sensor 11 (S1), and determines the sheet length L (S2). . Thereafter, when the user operates the operation panel 10 to select and input the type (material, basis weight) of the sheet P (S3), the control unit 9 selects a control mode based on the type of the sheet P. That is, when the material of the sheet P is an OHP film (S4: Y), or when the basis weight of the sheet P is 129 g / m ² or more (S5: Y), the first control mode is applied. (S6). When the sheet P is not an OHP film (S4: N) and the basis weight of the sheet P is less than 129 g / m ² (S5: N), the second control mode is applied (S7).

  When the first control mode is selected, the control unit 9 determines the feeding speed V1 (150 mm / sec) with reference to the table shown in Table 1 (S8). Then, the controller 9 starts driving the feed motor M1 and the extraction motor M2 with an output corresponding to the feed speed V1, and starts measuring the drive time of the feed motor M1 using the timer 13 (S9). If the front end of the sheet P is not detected by the feeding sensor 12 within a predetermined time (S10: N), it is determined that the feeding of the sheet P is delayed (delayed JAM) (S11), Initiate a jam handling process that includes a break in formation. When the feeding sensor 12 detects the front end of the sheet P within a predetermined time (S10: Y), the driving of the feeding motor M1 is stopped when the driving time of the feeding motor M1 becomes equal to the control time X1. (S12). As described above, the control time X1 is calculated as the time required for the sheet P to reach the first position.

  The control unit 9 keeps driving the drawing motor M2 and monitors the position of the sheet P using the feeding sensor 12. When the feeding sensor 12 detects the trailing edge of the sheet P and does not send an OFF signal within a predetermined time (S13: N), the control unit 9 is in a state where the sheet P stays inside the apparatus main body 201A. It is determined that it is in (Still JAM) (S14), and the jam processing process is started. When the feeding sensor 12 detects the trailing edge of the sheet P within a predetermined time (S13: Y), the sheet P is pulled after a time set so that the trailing edge of the sheet P passes through the drawing nip portion N2. The driving of the motor M2 is stopped (S15), and the feeding operation is completed.

  On the other hand, when the second control mode is selected, the control unit 9 determines the feeding speed V1 (250 mm / sec or 300 mm / sec) with reference to the table shown in Table 1 (S16). Then, the controller 9 starts driving the feed motor M1 and the extraction motor M2 with an output corresponding to the feed speed V1, and starts measuring the drive time of the feed motor M1 (S17). If the feeding sensor 12 does not detect the front end of the sheet P within a predetermined time (S18: N), the control unit 9 determines that the delay JAM state is present (S19) and starts the jam processing process. . When the feeding sensor 12 detects the front end of the sheet P within a predetermined time (S18: Y), the driving of the feeding motor M1 is stopped when the driving time of the feeding motor M1 becomes equal to the control time X2. (S20). As described above, the control time X2 is calculated as the time required for the sheet P to reach the second position.

  The control unit 9 keeps driving the drawing motor M2 and monitors the position of the sheet P using the feeding sensor 12. Then, if the trailing edge of the sheet P passes the feeding sensor 12 within a predetermined time and the feeding sensor 12 does not send an OFF signal (S21: N), the control unit 9 determines that it is in the staying JAM state. (S22) and the jam handling process is started. When the feeding sensor 12 detects the trailing edge of the sheet P within a predetermined time (S21: Y), the drawing motor is operated after a time set so that the trailing edge of the sheet P passes through the drawing nip portion N2. The driving of M2 is stopped (S23), and the feeding operation is completed.

  In this control process, a temporary stop process by inserting the front end of the sheet P against the registration roller pair 240 is appropriately inserted. This temporary stop processing is the operation of driving the registration roller pair 240 after stopping the drawing motor M2 at time Ts (see FIGS. 6 to 9) after the front end of the sheet P reaches the registration roller pair 240. This is a process of resuming driving in accordance with the start. However, when the timing at which the sheet P reaches the first position or the second position is after the pause processing (for example, in the case of FIG. 6), the control unit 9 resets the time measurement result by the timer 13, Based on the elapsed time from the time Tr, the driving of the feed motor M1 is stopped.

[Effect of this embodiment]
As described above, the sheet feeding apparatus 100A according to the present embodiment selects and executes the first control mode and the second control mode according to the type of the sheet P. When the stiffness of the sheet P is high (basis weight is large), the first control mode is selected, and the rear end of the sheet P is at the first position that is a predetermined distance upstream from the contact position of the pickup roller 2. In this state, the driving of the feeding motor M1 is stopped. That is, in the first control mode, the pickup roller 2 and the feed roller 3 are rotationally driven in the feeding direction within a range in which the sheet overlapping below the uppermost sheet P is not fed out. Thereby, by reducing the conveyance load applied to the drawing roller pair 8 due to the curvature of the sheet conveyance path, the weight of the sheet itself, and the like, it is possible to prevent the slip in the drawing nip portion N2 and stably convey the sheet.

  On the other hand, when the stiffness of the sheet P is low (basis weight is small), the sheet feeding device 100A selects the second control mode, and the front end of the sheet P is downstream by a predetermined distance from the drawing nip portion N2. The feed motor M1 is stopped driving in the second position. For this reason, when the sheet lengths are equal, the feeding motor M1 is stopped while the sheet P is in the second position upstream of the first position. That is, in the second control mode, the feeding motor M1 is stopped at an early timing within a range in which the sheet P does not fall off from the drawing nip portion N2. Thereby, since the driving force in the returning direction is not input to the retard roller 4, the occurrence of rotational vibration of the retard roller 4 is prevented. Even when the low-stiffness sheet P, which is likely to buckle, is conveyed, the time during which the retard roller 4 can generate rotational vibration is shortened, so that vibration noise can be reduced.

  Such a second control mode is generally applied to the low-stiffness sheet P having a small conveyance resistance as compared to the high-stiffness sheet P. For this reason, in the case of the sheet P with low rigidity, vibration noise can be reduced without impairing the stability of sheet conveyance. That is, the sheet feeding apparatus 100A according to the present embodiment can stably convey the sheet P and can reduce vibration noise during operation.

  In addition, when the second control mode is selected, the sheet feeding apparatus 100A according to the present embodiment conveys the sheet at a larger feeding speed V1 than when the first control mode is selected. Therefore, when the feed speed V1 is likely to cause the rotational vibration of the retard roller 4, the drive of the feed motor M1 is stopped at an earlier timing than when the feed speed is small. The vibration sound at the time can be reduced more effectively.

<Second Embodiment>
Next, a sheet feeding operation of the sheet feeding apparatus 100A according to the second embodiment will be described. The sheet feeding apparatus 100A according to the present embodiment is different from the first embodiment described above in that the feeding speed and the image forming speed are fixed, and the other points are the same as in the first embodiment. Configured. For this reason, elements having the same configuration and action are denoted by the same reference numerals and description thereof is omitted.

As in the first embodiment, the control unit 9 according to the present embodiment performs a process of selecting a control mode according to the type of the sheet P input by the user. That is, as shown in FIG. 11, when the user operates the operation panel 10 to select and input the type (material, basis weight) of the sheet P (S3), the control unit 9 sets the control mode in accordance with the selected and input information. Select (S4, S5). At this time, when the material of the sheet P is an OHP film (S4: Y), or when the basis weight of the sheet P is 129 g / m ² or more (S5: Y), the first control mode is selected. (S6). When the sheet P is not an OHP film (S4: N) and the basis weight of the sheet P is less than 129 g / m ² (S5: N), the second control mode is selected (S7). Then, under the feeding speed commonly used in the first and second control modes, the feeding motor M1 and the drawing motor M2 are started to start conveying the sheet P (S9, S17).

  The information referred to when selecting the control mode is not limited to the combination of the material of the sheet P (whether it is an OHP film) and the basis weight, but may be other information. For example, the control mode may be selected based only on the basis weight, or the control mode may be selected by combining the classification of high-quality paper / recycled paper / coated paper and the basis weight. In short, any configuration may be used as long as the first control mode is applied to the sheet P with high rigidity and the second control mode is applied to the sheet P with low rigidity.

[Effect of this embodiment]
Since the sheet feeding apparatus 100A according to the present embodiment is configured to select the control mode according to the type of the sheet P, the sheet feeding apparatus 100A is applied to an image forming apparatus in which the feeding speed V1 and the image forming speed V2 are fixed. Can do. The sheet feeding apparatus 100A performs the sheet feeding operation by switching between the first control mode and the second control mode in accordance with the stiffness of the sheet. Similar effects can be obtained. That is, the sheet feeding device 100A can stably convey the sheet P and can reduce vibration noise during operation.

<Third Embodiment>
Next, the sheet feeding operation of the sheet feeding apparatus 100A according to the third embodiment will be described. The sheet feeding apparatus 100A according to the present embodiment is different from the first embodiment described above in that the driving stop timing of the feeding motor M1 is determined based on the detection signal of the feeding sensor 12. Since the other points are configured in the same manner as in the first embodiment, elements having the same configuration and action are denoted by the same reference numerals and description thereof is omitted.

[When the sheet is large]
First, a sheet feeding operation when a relatively large sheet P having a sheet length L1 is conveyed will be described with reference to FIG. However, FIG. 12 is a diagram in which a diagram representing a change in the position of the sheet P is combined with a timing chart representing drive control of the feeding motor M1 and the pulling motor M2. A broken line D2 in the drawing indicates the output of the feed motor M1 in the second control mode as a difference with respect to the output D in the first control mode. A broken line F in the drawing represents the front end position of the sheet P when the sheet is conveyed later than the maximum delay line A2.

  As shown in FIG. 12, when the first control mode is applied, the feed motor M1 starts driving at time Tf together with the pulling motor M2, and then temporarily stops at time Ts. The feed motor M1 is stopped at the timing (time T6) when the control time X1 has elapsed after being restarted at time Tr in accordance with the start of driving of the registration roller pair 240. However, the control time X1 is a time calculated so that the trailing edge of the sheet P reaches a position upstream of the contact position of the pickup roller 2 by a predetermined distance (first position) under the image forming speed V2. .

  On the other hand, when the second control mode is applied, the feed motor M1 starts to be driven at time Tf, and the timing (time when the control time X2 has elapsed since the feed sensor 12 issued the ON signal at time Ta. The driving is stopped at T5) (broken line D2). However, the control time X2 is a position (second position) where the front end of the sheet P is a predetermined distance downstream from the drawing nip portion N2 under the feeding speed V1 after the feeding sensor 12 detects the front end of the sheet P. Is the time calculated to reach Accordingly, when the front end of the sheet P is conveyed later than the maximum delay line A2 as indicated by a broken line F, the feeding motor M1 stops at a later timing (time T5) than in the first embodiment. (See time T2 in FIG. 7).

[When the sheet is small]
Next, a sheet feeding operation when a relatively small sheet P having a sheet length L2 smaller than L1 is conveyed will be described with reference to FIG. However, FIG. 13 is a diagram in which a diagram representing a change in the position of the sheet P is combined with a timing chart representing drive control of the feeding motor M1 and the pulling motor M2. A broken line D2 in the drawing indicates the output of the feed motor M1 in the second control mode as a difference with respect to the output D in the first control mode. A broken line F in the drawing represents the front end position of the sheet P when conveyed earlier than the theoretical line A1, and a broken line G represents the rear end position of the sheet P in this case.

  As shown in FIG. 13, when the first control mode is applied, the feed motor M1 starts driving at the time Tf together with the pulling motor M2, and after the feed sensor 12 issues an ON signal at the time Ta. The drive is stopped at the timing (time T8) when the control time X1 has elapsed. However, the control time X1 is a time calculated so that the trailing edge of the sheet P reaches a position upstream of the contact position of the pickup roller 2 by a predetermined distance (first position) under the feeding speed V1. . Therefore, when the sheet P is conveyed earlier than the theoretical line B1, the feeding motor M1 is stopped at an earlier timing (time T8) than that of the first embodiment (see time T3 in FIG. 8). ).

  On the other hand, when the second control mode is applied, the feed motor M1 starts to be driven at time Tf, and the timing (time when the control time X2 has elapsed since the feed sensor 12 issued the ON signal at time Ta. The driving is stopped at T7) (broken line D2). However, the control time X2 is a time calculated so that the front end of the sheet P reaches a position (second position) downstream of the drawing nip portion N2 by a predetermined distance under the feeding speed V1. Accordingly, when the sheet P is conveyed earlier than the theoretical line A1, the feeding motor M1 is stopped at an earlier timing (time T7) than that of the first embodiment (see time T4 in FIG. 9). ).

[Control flow]
As shown in the flowchart of FIG. 14, the control unit 9 according to the present embodiment starts timing by the timer 13 on the condition that the feed sensor 12 has issued an ON signal (S10: Y, S18: Y). (S24, S25). When the first control mode is applied, the feeding motor M1 is stopped at the timing when the control time X1 has elapsed from the start of timing (S12). When the second control mode is applied, the feeding motor M1 is stopped at the timing when the control time X2 has elapsed from the start of timing (S20).

[Effect of this embodiment]
Since the sheet feeding apparatus 100A according to the present embodiment determines the feeding speed V1 according to the stiffness of the sheet P and selects the control mode according to the value of the feeding speed V1, the above-described first The same effect as that of the first embodiment can be obtained. That is, the sheet feeding device 100A can stably convey the sheet P and can reduce vibration noise during operation.

  By the way, as shown in FIG. 12, when the sheet P is set at a position shifted from the design setting position of the feeding cassette 7 (broken line F), the front end of the sheet P is conveyed with a delay from the maximum delay line A2. May be. In such a case, in the configuration in which the stop timing of the feeding motor M1 is determined based on the maximum delay line A2, the driving of the feeding motor M1 is stopped before the sheet P is delivered to the drawing nip portion N2. There is a possibility that the sheet P stays inside the apparatus. On the other hand, in the sheet feeding apparatus 100A according to the present embodiment, the stop timing of the feeding motor M1 is delayed according to the delay of the sheet P based on the detection signal of the feeding sensor 12. For this reason, even if the sheet P is behind the normal range, the sheet P can be reliably delivered to the drawing nip portion N2.

  Further, as shown in FIG. 13, when the sheet P is set at a position shifted from the set position (broken lines F and G), the sheet P is conveyed earlier than the theoretical lines A1 and B1 (early arrives). )Sometimes. In such a case, in the configuration in which the stop timing of the feeding motor M1 is determined based on the theoretical line B1, the feeding is performed despite the actual trailing end of the sheet P moving downstream from the pickup roller 2. There is a possibility that the driving of the motor M1 is continued. When the driving of the feeding motor M1 is continued in this way, the pickup roller 2 feeds out a sheet (next sheet) that overlaps the uppermost sheet. Then, when the next sheet P is displaced downstream from the normal position, the next sheet P is further displaced, and the positional deviation of the sheets P may be piled up to hinder the sheet feeding operation. . On the other hand, in the sheet feeding apparatus according to the present embodiment, the stop timing of the feeding motor M1 is advanced according to the early arrival timing of the sheet P based on the detection signal of the feeding sensor 12. For this reason, even when the sheet P arrives early beyond the normal range, the next sheet P is prevented from being displaced, and the sheet feeding apparatus 100A can stably perform the sheet feeding operation. be able to.

<Fourth Embodiment>
Next, a sheet feeding operation of the sheet feeding apparatus 100A according to the fourth embodiment will be described. The sheet feeding apparatus 100A according to the present embodiment stops driving the feeding motor M1 based on the detection signal from the feeding sensor 12 as in the third embodiment described above. This is different from the third embodiment in that the feeding speed is changed in the middle of the process. Hereinafter, elements having the same configuration and operation as those of the third embodiment are denoted by the same reference numerals and description thereof is omitted.

  FIG. 15 is a diagram in which a diagram representing a change in the position of the sheet P is combined with a timing chart representing drive control of the feeding motor M1 and the drawing motor M2. A broken line D2 in the drawing indicates the output of the feed motor M1 in the second control mode as a difference with respect to the output D in the first control mode. A locus H indicated by a broken line in the drawing exemplifies a locus that the front end of the sheet P actually follows.

  As shown in FIG. 15, when the feeding sensor 12 detects the front end of the sheet P, the control unit 9 changes the driving speeds of the feeding motor M1 and the drawing motor M2 from V1 to V3 according to the detection timing. At this time, when the detection timing is delayed with respect to the theoretical line A1 as in the locus H, the drive speed is increased from V1, and when the detection timing is earlier than the theoretical line A1, the drive is performed. The speed is reduced from V1. That is, the control unit 9 feeds the feeding motor M1 and the drawing motor M2 so as to absorb variations in elapsed time from when the feeding motor M1 starts to be driven until the feeding sensor 12 detects the front end of the sheet P. The drive speed is changed.

  By the way, when the drive speeds of the feeding motor M1 and the drawing motor M2 are shifted from V1 to V3, the speed changes during a shift time T that is a time width determined by the response characteristics of these motors. During this speed change time T, the torque load in the feed direction transmitted to the retard roller 4 fluctuates irregularly. Further, since the response of the torque limiter 5 to the fluctuation of the torque load is usually accompanied by a certain delay, the force in the returning direction that acts on the sheet P from the retard roller 4 during the shift time T as compared with the time before and after that. Becomes unstable. When such a shift is performed in a state in which the driving force in the returning direction is not input to the retard roller 4, there is a possibility that double feeding of sheets occurs.

  Therefore, the sheet feeding apparatus 100A according to the present embodiment is set so that the stop timing of the feeding motor M1 is after the completion of the shift when at least the second control mode is applied. That is, as shown in FIG. 15, after the feeding sensor 12 detects the front end of the sheet at time Ta and the shift of the driving speed is started, the control time X2 longer than the shift time T has elapsed (time T9). ), The driving of the feeding motor M1 is stopped (see the broken line D2). However, the control time X2 is a time calculated so that the front end of the sheet P reaches a position (second position) downstream from the drawing nip portion N2 by a predetermined distance. On the other hand, when the first control mode is applied, the rear end of the sheet P is located at a position upstream of the contact position of the pickup roller 2 by a predetermined distance (first position), as in the third embodiment described above. ) Is stopped (time T10), the driving of the feeding motor M1 is stopped.

[Control flow]
As shown in FIG. 16, the control unit 9 according to the present embodiment changes the speeds of the feed motor M1 and the extraction motor M2 on the condition that the feed sensor 12 generates an ON signal (S10: Y, S18: Y). And the time measurement by the timer 13 is started (S26, S27). Then, after waiting for the shift from V1 to V3 to be completed (S28, S29), the feeding motor M1 is stopped at the timing when the control times X1, X2 have elapsed from the start of timing (S12, S20).

[Effect of this embodiment]
The control unit 9 of the sheet feeding apparatus 100A according to the present embodiment changes the drive speeds of the feeding motor M1 and the pulling motor M2 based on the detection signal from the feeding sensor 12. As a result, the variation in elapsed time from the start of the sheet feeding operation (time Tf) until the front end of the sheet P reaches the registration roller pair 240 can be kept within a small range. When the plurality of sheets P are continuously conveyed, the interval between the sheets can be narrowed to improve the productivity of the image forming apparatus 201.

  In such a configuration, the stop timing of the feeding motor M1 is set after the shifting of the feeding motor M1 and the drawing motor M2 is completed and after the sheet P reaches the second position. Therefore, during the shift time T during which multiple feeds are likely to occur, a return driving force is applied to the retard roller 4 to prevent double feed, and after completion of the shift, the drive of the feed motor M1 is immediately stopped to vibrate. Generation of sound can be prevented.

  If the stop timing of the feed motor M1 in the second control mode is configured after the completion of the shift and after the sheet P reaches the second position, for example, the feed sensor 12 is connected to the pulling nip portion N2. You may arrange | position in the downstream of. On the other hand, in the above-described embodiment, the feeding sensor 12 is disposed between the separation nip portion N1 and the drawing nip portion N2 in the feeding direction (see FIG. 3), and the front end of the sheet P is located at the drawing nip portion N2. Before reaching, the shifting of the feeding motor M1 and the drawing motor M2 is completed. For this reason, as compared with the third embodiment, it is preferable that the driving time of the feeding motor M1 is not extended by waiting until the shift is completed.

<Other embodiments>
In the first to fourth embodiments described above, the driving means is provided as a single motor. However, the driving means (motor) for driving the feed roller 3 and the driving means (motor) for driving the retard roller 4 are provided. May be provided separately. In this case, the stop timing of the feeding motor M1 may be read as the timing at which these motors are all stopped.

  The configuration is not limited to the configuration in which the drawing roller pair 8 is positioned downstream of the feed roller 3 and the retard roller 4, but may be a configuration in which, for example, a registration roller pair is positioned. In short, what is necessary is just a structure provided with the conveyance means which has a conveyance nip part which clamps the sheet | seat P downstream from the separation nip part N1, and conveys a sheet | seat.

  2 ... pickup roller / 3 ... feed roller (feed roller) / 4 ... separation roller (retard roller) / 5 ... torque limiter / 7 ... stacking means (feed cassette) / 8 ... conveying means (drawing roller pair) / 9 ... Control means (control unit) / 10 ... Input means (operation panel) / 11 ... Size detection means (size detection sensor) / 12 ... Sheet detection means (feed sensor) / 13 ... Time measurement means (timer) / 100A, 100B , 100C, 100D ... sheet feeding apparatus / 201 ... image forming apparatus / 201B ... image forming means (image forming part) / M1 ... driving means (feed motor) / N1 ... separation nip part / N2 ... conveying nip part (drawing) Nip part) / P, P1, P2, Q1, Q2 ... sheet / Fd ... feed direction

Claims (17)

A feeding roller for conveying the sheet in the feeding direction;
Driving means for driving the feeding roller;
A separation nip portion that sandwiches the sheet between the feeding roller and a separation roller that is connected to the driving means via a torque limiter and is driven in a direction against the feeding direction;
A transport unit having a transport nip portion that sandwiches the sheet downstream of the separation nip portion in the feeding direction, and transports the sheet;
After starting the drive of the driving means, a control means for stopping the driving of the drive means in a state in which the seat is sandwiched the separation nip portion and the conveying nip, the you convey the first sheet in one control mode, and a Ru control means stops the driving of the second of said drive means at a timing later than the control mode for conveying the second sheet basis weight is less than the first sheet Prepare
A sheet feeding apparatus characterized by that. A feeding roller for conveying the sheet in the feeding direction;
Driving means for driving the feeding roller;
A separation nip portion that sandwiches the sheet between the feeding roller and a separation roller that is connected to the driving means via a torque limiter and is driven in a direction against the feeding direction;
A transport unit having a transport nip portion that sandwiches the sheet downstream of the separation nip portion in the feeding direction, and transports the sheet;
After starting the drive of the driving means, a control means for stopping the driving of the drive means in a state in which the seat is sandwiched the separation nip portion and the conveying nip, the you convey the first sheet in one control mode, and a Ru control means stops the driving of said driving means at a timing later than the second control mode for conveying stiffness is lower second sheet than the first sheet ,
A sheet feeding apparatus characterized by that.   When the control unit selects the first control mode when the lengths of the first sheet and the second sheet in the feeding direction are equal to each other, the first sheet is in the first position. When the driving of the driving unit is stopped and the second control mode is selected, the driving of the driving unit is stopped in a state where the second seat is in the second position upstream from the first position.
  The sheet feeding apparatus according to claim 1 or 2. The control means, when selecting the second control mode, causes the drive means to drive the feeding roller at a higher speed than when selecting the first control mode.
The sheet feeding apparatus according to any one of claims 1 to 3 . In the second control mode, the control unit stops the driving of the driving unit in a state where the central portion of the sheet in the feeding direction is closer to the separation nip than the conveyance nip.
The sheet feeding apparatus according to any one of claims 1 to 4 . In the second control mode, the control unit stops the driving of the driving unit at a timing at which the front end of the sheet is separated from the conveyance nip portion in the range of 10 mm to 20 mm downstream in the feeding direction.
The sheet feeding apparatus according to any one of claims 1 to 5 . A stacking means on which sheets are stacked;
Size detecting means for detecting the length in the feeding direction of the sheets stacked on the stacking means,
The control means, when selecting the first control mode, stops driving of the drive means based on a detection signal from the size detection means,
The sheet feeding apparatus according to any one of claims 1 to 6 .   A pickup roller capable of contacting the sheet at a contact position upstream of the separation nip portion in the feeding direction and transporting the sheet in the feeding direction;
  The control unit stops driving of the driving unit based on a timing at which a rear end of the first sheet reaches the contact position in the first control mode;
  The sheet feeding apparatus according to any one of claims 1 to 7. A pickup roller capable of contacting the sheet at a contact position upstream of the separation nip portion in the feeding direction and transporting the sheet in the feeding direction;
In the first control mode, the control unit stops driving of the driving unit in a state where a center portion of the sheet in the feeding direction is closer to the conveyance nip than the contact position.
The sheet feeding apparatus according to any one of claims 1 to 8 . In the first control mode, the control means drives the drive means in a state where the trailing edge of the sheet is separated from the contact position in the range of 10 mm or more and 20 mm or less upstream in the feeding direction. To stop ,
The sheet feeding apparatus according to claim 9 .   A registration unit that is disposed downstream of the conveyance nip portion in the feeding direction and conveys the sheet received from the conveyance unit;
  When the first control mode is selected when the first sheet is longer than the distance between the pickup roller and the registration unit, the control means is configured to allow the front end of the first sheet to reach the registration unit. Stopping driving of the driving means, and stopping driving of the driving means before the front end of the second sheet reaches the registration unit when the second control mode is selected;
  The sheet feeding apparatus according to claim 9.   A motor for driving the conveying means;
  The driving means comprises a single motor provided separately from the motor,
  The sheet feeding apparatus according to any one of claims 1 to 11. Comprising input means capable of inputting the type of sheet conveyed by the feeding roller;
The control means selects the first control mode or the second control mode based on the type of sheet input to the input means.
The sheet feeding apparatus according to any one of claims 1 to 12 . Comprising time measuring means capable of measuring the time elapsed since the driving of the driving means was started,
The control means stops driving of the driving means based on a signal from the time measuring means.
The sheet feeding device according to any one of claims 1 to 13 . A sheet detecting means disposed downstream of the separation nip portion in the feeding direction and capable of detecting a sheet;
A timing means capable of measuring the time elapsed since the front end of the sheet was detected by the detection means,
The control unit stops driving of the driving unit based on signals from the sheet detecting unit and the time measuring unit.
Sheet feeding apparatus according to any one of claims 1 to 1 4. The control means absorbs the variation in elapsed time from the start of driving of the driving means until the sheet detecting means detects the front end of the sheet based on the detection signal from the sheet detecting means. The sheet conveying speed of the conveying unit is changed, and after the shifting of the conveying unit is completed, the driving of the driving unit is stopped.
Sheet feeding apparatus according to claim 1 5. The sheet feeding device according to any one of claims 1 to 16 ,
An image forming apparatus comprising: an image forming unit that forms an image on a sheet supplied from the sheet feeding device.

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